This project is concerned with analysis of the diversity of medically important parasitic protozoa and its implications to the epidemiology, course, and diagnosis of disease, the development and utilization of atomic force microscopy (AFM) for the study of infectious diseases, the development of high resolution, low-light-level video microscopy for the study of the interaction of parasitic protozoa with host cells, and analyses of host-parasite interactions at cellular and subcellular levels. We have developed methodology to perform AF Microscopy on living cells. The methodology has been used to study the course of infection of vertebrate cells with Trypanosoma cruzi and Toxoplasma gondii. In addition, we have developed a mathematical model of AFM-derived force curves. The model has been used to analyze the kinetics of cell division.